1. Field of the Invention
The present invention relates to a solid electrolytic capacitor in which a solid electrolyte is a conductive polymer, and a production method of the same.
This application is based on patent application No. Hei 10-101186 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
Metallic oxides such as manganese dioxide, tetracyanoquinodimethane complex, and the like have been used as a solid electrolyte comprising a solid electrolytic capacitor, and recently, a solid electrolytic capacitor in which a solid electrolyte is used as a conductive polymer (abbreviated as "solid electrolytic capacitor") has been suggested.
One characteristic of the solid electrolytic capacitor is that the equivalent series radiation (abbreviated as "ESR") is low. In order to make the ESR of the solid electrolytic capacitor low, it is necessary that the ESR of a cathode layer is also low; therefore, a thermosetting graphite paste layer (abbreviated as "Gr paste layer") is used to the cathode layer.
However, conductive polymers which are organic semiconductors are used as solid electrolytes in the conventional solid electrolytic capacitors. Therefore, when the solid electrolytic capacitor is left in air at high temperatures for long periods, the solid electrolyte is oxidation degraded, and then the ESR thereof becomes high.
That is, the thermosetting materials used in a Gr paste layer comprising a conventional solid electrolytic capacitor generally does not have heat resistance. Temperature stress generatied in packaging makes cracks and peels in the Gr paste layer; therefore, oxygen access channels are newly formed therein. Consequently, the solid electrolyte layer comprised of a conductive polymer is easily oxidization degraded.
Moreover, in order to make the ESR of the solid electrolytic capacitor low, Japanese Patent Application, First Application No. Hei- 08-162371, paid attentions to improving the contact between the Gr layer and the conductive layer. The application suggested that the solid electrolytic capacitor in which the Gr layer contains the graphite paste comprising acrylic resins. In addition, the solid electrolytic capacitor comprising the Gr layer having a thickness in a range of 5 to 10 .mu.m, which is thinner than the thickness of the conventional Gr layer, is suggested. The object could be achieved, because the Gr layer having such thickness acts as a grounding for the conductive layer, that is, has an anchoring effect for the conductive layer.
It is therefore an object of the present invention to provide a solid electrolytic capacitor which can prevent an oxidation degradation of a solid electrolyte caused by heat stress and the like during packaging, which has low an ESR, and a production method of the same.